Mechanical safety interlock for covers of explosionproof electrical housing

ABSTRACT

An explosionproof electrical enclosure has a body with two caps threaded on opposite ends of the body. Within the body is an electrical switch operable by a handle positioned outside the body. The caps are held against rotation by pins which extend through the body and are resiliently urged into recesses in the caps. These pins are accessible from outside the body so that they can be moved out of the recesses thereby allowing the caps to be rotated and unthreaded. A second set of pins adjacent and parallel to the first are moved longitudinally by the caps when the caps are removed or replaced. A safety interlocking mechanism includes plates positioned adjacent the inner ends of the pins and movable coincident with the turning of the handle between the switch-open and the switch-closed position. This interlocking mechanism prevents the first pins from being unseated from the cap recesses so long as the electrical switch is closed and prevents the handle from being turned from the switch-open to the switch-closed position so long as one or both of the second pins detects the absence of a cap.

United States Patent [191 Appleton et a1.

MECHANICAL SAFETY INTERLOCK FOR COVERS 0F EXPLOSIONPROOF ELECTRICALHOUSING Filed:

Appl. No.: 258,983

Inventors: Arthur L. Appleton,Northbrook;

Robert Pastorelt @5959: eihe lll.

Assignee: Appleton Electric Company,

Chicago. 111.

June 2, 1972 July 3, 1973 l 5 7 1 ABSTRACT An explosionproof electricalenclosure has a body with two caps threaded on opposite ends of thebody. Within the body is an electrical switch operable by a handlepositioned outside the body. The caps are held against rotation by pinswhich extend through the body and are resiliently urged into recesses inthe caps. These pins are accessible from outside the body so that they'can be moved out of the recesses thereby allowing the caps to berotated and unthreaded. A second set of pins adjacent and parallel tothe first are moved longitudinally by the caps when the caps are removedor replaced. A safety interlocking mechanism includes plates positionedadjacent the inner ends of the pins and movable coincident with theturning of the handle between the switch-open and the switch-closedposition. This interlocking mechanism prevents the first pins from beingunseated from the cap recesses so long as the electrical switch isclosed and prevents the handle from being turned from the switch-open tothe switch-closed position so long as one or both of the second pinsdetects the absence of a cap.

5 Claims, 7 Drawing Figures Patented July 3, 1973 3,743,00

2 Sheets-Sheet 8 WITH ' ununun 1 nnnnzn III II ELECTRIC SWITCH A: v q.'1

MECHANICAL SAFETY INTERLOCK FOR COVERS OF EXPLOSIONPROOF ELECTRICALHOUSING BACKGROUND AND SUMMARY OF THE INVENTION The present invention isan improvement on the apparatus of U. S. Pat. No. 3,582,535. In theapparatus of that patent there is an electrical housing having capswhich are threaded over openings on opposite sides of the housing. Thesecaps have pins which seat in recesses in the housing to locate the capsin a proper rotational position on the housing. The pins are movedlongitudinally to withdraw them from the recesses and thereby permit thecaps to be unthreaded for removal from the housing body.

The present invention is an improvement on that apparatus. In the firstplace it prevents the pins from being unseated from the recesses unlessthe electrical switch within the housing has been moved to theswitch-open position so that the electrical circuits accessible when thecap is removed will be deenergized. Secondly, the safety interlock ofthe present invention prevents the electrical switch from being closedso long as the caps have not been put fully into place to make thehousing explosionproof. A further feature of the invention is that thepins that must be unseated to permit the unthreading of the caps areconcealed and access thereto is not readily apparent. This preventstampering by someone who is not fully familiar with the apparatus.

The present invention relates to a safety interlock for caps threadedlymounted on an explosionproof housing body, which interlock is simple yeteffective to guard against the dangers present with electrical devicesinstalled in a flammable atmosphere.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of anembodiment of the invention;

FIG. 2 is an enlarged partial side view showing portions broken away asseen at line 2--2 of FIG. 1;

FIG. 3 is a fragmentary view illustrating the operation of the safetyinterlock and showing the parts as positioned when the covers are inplace and the electrical switch closed;

FIG. 4 is a fragmentary view corresponding to FIG. 3 but showing theposition of the parts with a cover removed and the switch in the opencircuit position;

FIG. 5 is a sectional view of the housing body and interlockingapparatus as seen at line 5-5 of FIG. 2;

FIG. 6 is a section as seen at line 6-6 of FIG. 5; and

FIG. 7 is an enlarged sectional view as seen at line 7-7 of FIG. 6.

DESCRIPTION OF SPECIFIC EMBODIMENT The following disclosure is offeredfor public dissemination in return for the grant of a patent. Althoughit is detailed to ensure adequacy and aid understanding, this is notintended to prejudice that purpose of a patent which is to cover eachnew inventive concept the body. About these openings are collars 13 and13. The exteriors of the collars are in the form of truncated cones andhave threads 14 and 14' thereon. The bottom portions of the caps 11, 11are of a corresponding configuration and have threads 15, 15' which matewith and engage threads 14, 14'. Around the bottoms of the caps areperipheral flanges l6, 16. At the front, the body 10 has a rectangularprojection 17.

There are recesses 20, 20 in the end faces of the flanges l6, 16'. Ateach of these recesses a small opening 21, 21' extends through theflange. These recesses cooperate with pins 22, 22' to properly positionthe caps in an explosionproof, but not jamming, position on the body.This is explained more fully in US. Pat. No. 3,582,535.

As best seen in FIG. 7, the pins have a shoulder 23. A spring 24 bearsagainst this shoulder and against the end of a plug 25 of a mounting 26.The pin 22 is movable longitudinally thereof within the openings inmounting 26 and plug 25. It is urged outwardly by the spring 24. In theoutward position it will seat in the recesses 20, 20' of the caps.

Within the housing is an electric switch 28. It is operatively connectedto a crank 29 secured to the end of a shaft 30. The shaft 30 isjournaled in the projection 17 of the body 10. At the outside end of theshaft a handle 31 is secured thereto. A movement of the shaft in theclockwise direction, as viewed in FIGS. 1 and 5, turns the switch 28 toa position such that the electrical circuits within the housing are hot,that is, energized. A rotation of the handle 31 in the counterclockwisedirection actuates switch 28 so that the accessible electric circuitswithin the housing are dead, that is, deenergized.

There is a second pair of pins 33, 33 which serve as sensors for thepresence or absence of the caps on the body. These pins are journaled inmountings 34, 34' and plugs 35, 35'. At the inner ends these pins haveheads 36, 36 forming abutments. They also have shoulders 37. A spring 38is in compression between shoulder 37 and the end of plug 35 (FIG. 7).

U-shaped brackets 40, 40' are held by the mountings 26, 26', 34, 34 andthe plugs 25, 25, 35, 35. Adjacent the distal ends of the brackets 40,40' are slots 41, 41 through which plates 42, 42' slide. One end of eachplate is formed into a hook and these have openings 43, 43 therethrough.A link 44 has two arms 45 and 45'. The arm 45 extends upwardly throughopenings 43 in plate 42 and the arm 45' extends downwardly through theopenings 43 in plate 42'. A pin 46 pivotally connects link 44 to a crank47 on shaft 30.

The distal ends of plates 42, 42' are bifurcated. Adjacent the ends theyhave relatively wide slots 49, 49'. Near the centers of the plates arecomparatively narrow slots 50, 50'. The relatively wide slots areslightly wider than the diameters of the heads 36, 36' of the pins 33,33'. The relatively narrow slots 50, 50 are just slightly wider than thediameters of pins 22, 22', but smaller than the diameters of the heads36, 36'. From the slots toward the other end there are third areas 51,51' which are completely closed. These serve as a stop or an abutment toblock movement of pins 22, 22', as hereinafter described.

OPERATION Assume that the housing is closed, as illustrated in FIG. 1,and that the handle 31 is positioned so that the electric switch 28 isclosed, energizing the accessible electrical components within thehousing. The housing is explosion-proof; that is, should flammablevapors obtain access to the interior of the housing and be ignitedtherein, the resultant flame will not propagate outside of the housing.The pins 22, 22' are extended into the recesses 20, in the caps, thusrestraining the caps against rotation. The closed areas 51, 51 arealigned with the pins 22, 22 (as illustrated in FIG. 3) so that the pinsmay not be moved inwardly to unseat the pins from the recesses 20, 20'of the caps 11, 11'. Thus, it is not possible to remove the caps. Theflanges 16, 16' are pressing against the adjacent ends of pins 33, 33and have moved the pins toward each other against the urging of springs38, 38'. Thus, the heads 36, 36' of the pins 33, 33' are clear of plates42, 42, as seen in FIG. 2 and as illustrated in dotted lines in FIG. 7.Therefore, neither pins 22, 22' nor pins 33, 33' are interfering withthe movement of plates 42, 42'. Handle 31 is free to rotate shaftbetween the switch-on position and the switch-off position.

Now if it is desired to remove one or both of caps 11, 11, the handle 31is turned counterclockwise to rotate shaft 30 to the switch-offposition. This moves the plates 42, 42 from the position illustrated inFIG. 3 to the position illustrated in FIGS. 4-7. Here the relativelynarrow slots 50, 50 are aligned with pins 22, 22. It is now possible forthe workman to insert a narrow object (e.g. asmall screwdriver, a nail,etc.) through opening 21 in flange 16 and push pin 22 downwardly out ofrecess 20. At the same time cap 11 can be rotated to disengage thethreads and remove the cap. Similarly, the narrow object can then beinserted through the small inconspicuous opening 21' of cap 11 to pushpin 22' inwardly and release cap 11 for rotation in a thread disengagingdirection. The removal of cap 11 allows spring 38 to move pin 33outwardly. At the same time, the head 36 on the pin 33 moves into therelatively large slot 49 of the plate 42. Also, the removal of cap 11'frees pin 33 so that head 36 thereof moves into slot 49' ofplate 42.Thus, with either of the caps 11, 11' removed, the respective pin 33, 33moves into a position at which the head 36, 36 thereof blocks the returnmovement of plate 42, 42'. For example, referring to FIGS. 4 and 7, theplates 42, 42' cannot be moved to the right. Thus, shaft 30 cannot nowbe rotated from the switch-off to the switch-on position.

With the covers off, it would be possible to manually depress both ofpins 33, 33', thereby permitting movement of the handle 31 toward theposition at which the switch 28 is closed. However, it is exceedinglyawkward for this operation to be performed. It could not be doneaccidentally, but only when a knowledgeable individual was working aboutthe apparatus and was satisfied that it was safe to close switch 28.

With the caps removed and the interlocking device in the positionillustrated in FIGS. 4-7, the return of the caps push the pins 33, 33'inwardly so that the heads 36, 36 thereof are clear of the plates 42,42'. When, during the same act of returning the caps onto the body, theproper degree of thread engagement is achieved, the pins 22, 22 snapoutwardly into the recesses 20, 20' of the caps. This then locks thecaps in that proper position of engagement. Prior to this time, eitheror both of pins 22, 22' or 33, 33 are positioned in the paths ofmovements of the plates 42, 42' so that the handle 31 cannot be moved inthe direction of rotation towards the switch-on position. Thus, forexample,

with the cap 11 almost in place so that it is depressing pin 33, but notsufficiently in place so that pin 22 is in recess 20, the flange 16 willhave depressed pin 22 to the same extent that it depressed pin 33. Thiswill have caused pin 22 to move into the dotted line positionillustrated in FIG. 7 at which position it is blocking the movement ofplate 42, even though the head 36 of pin 33 may have cleared the plate42 for movement. With both of the covers fully in place, the plates 42,42' are free to slide to the right from the positions illustrated inFIGS. 4-7. This permits the handle 31 to be rotated to the switch-onposition. In this latter position the slides are now in the FIG. 3position. Again, the covers are locked against removal since pins 22,22' cannot be moved inwardly to release the covers.

We claim:

1. In an explosionproof electrical enclosure apparatus comprising ahousing having a body with an opening with threads therearound and a capthreaded onto said threads and covering said opening, an electricalswitch within said housing and operable between a switchopen positionand a switch-closed position, said switch having a member within saidhousing for moving the switch between said positions which member isoperable from outside said housing, a locking device interengaging saidcap of said housing and movable between a first position at which saidcap is locked at a desired location against rotation and a secondposition at which said cap is free to be rotated to unthread the cap forremoval to expose said opening, said locking device being operable fromoutside said housing, the improvement comprising:

interlocking means operatively interconnecting the switch operatingmember and said cap locking device for retaining said locking device insaid first position so long as the member is in the switchclosedposition while freeing the locking device for movement to the secondposition so long as the member is in the switch-open position, and fornormally blocking the member for movement from switch-open toswitch-closed position so long as the cap is off the body, saidinterlocking means including a sensor positioned to be contacted by saidcover and in a first position when said cover is in place and to bemoved to a second position when said cover is off the body;

said locking device including a first pin in said body and movable in adirection generally parallel to the axis of the threads between ablocking position and an unblocking position, said cap having abutmentmeans positioned adjacent the pin when the cap is in place and said pinis in the blocking position to prevent rotation of the cap to unthreadthe cap from the body, resilient means bearing on the pin to urge thepin to said blocking position, said pin being movable against saidresilient means to said unblocking position at which said cap may berotated;

said sensor including a second pin on said body, movable in a directiongenerally parallel to the axis of the threads and positioned so that oneend of the second pin will contact said cap when said cap is in place,resilient means bearing against the second pin and urging it in thedirection of said one end, whereby said second pin is held in a firstposition by the pressure of said cap when the cap is in place and ismoved to a second position by the lastmentioned resilient means when thecap is removed; and

said interlocking means including a plate movable in said housing andhaving portions adjacent said pins, said plate being connected to saidmember. 2. In an apparatus as set forth in claim 1, wherein said pinseach have a longitudinal axis, said plate being movable in a planeintersecting said axes between a first position at which the member isin the switchclosed position and a second position at which the memberis in the switch-open position, said plate having a closed area alignedwith the axis of the first pin when the member is in the switch-closedposition with said closed area being positioned to block movement of thefirst pin from the blocking to the unblocking position, said platehaving an open area aligned with the axis of the first pin when themember is in the switchopen position with said open area unblocking saidfirst pin so that it may be moved to the unblocking position, saidsecond pin having an abutment thereon which abutment is moved with thesecond pin, said abutment being positioned to block the movement of theplate from the switch-open to the switch-closed position when the secondpin is in its second position, said abutment being moved to anunblocking position when the second pin is moved to the first position.

3.1m an apparatus as set forth in claim 2, wherein said cap has a flangethereon, said abutment means being in the side of said flange adjacentsaid body, said flange having a small opening extending from saidabutment means to the other side of the flange, whereby a small objectmay be inserted through said small opening to move the first pin fromthe blocking to the unblocking position.

4. In an apparatus as set forth in claim 2, wherein as said cap is movedtoward said desired location by the rotation of said cap and said secondpin is being moved from said second position toward said first positionto release said plate, said first pin is simultaneously being moved bythe cap into a position at which it blocks the movement of the plateuntil the cap reaches said desired location and the first pin engagessaid abutment means thereby moving the first pin out of blockingposition to free said plate.

5. In an apparatus as set forth in claim 1, wherein said cap has aflange thereon, said flange having a recess in the side of said flangeadjacent said body and defining said abutment means, said flange havinga small opening extending from said recess to the other side of theflange, whereby a small object may be inserted through said smallopening to move the first pin from the blocking to the unblockingposition.

1. In an explosionproof electrical enclosure apparatus comprising ahousing having a body with an opening with threads therearound and a capthreaded onto said threads and covering said opening, an electricalswitch within said housing and operable between a switch-open positionand a switch-closed position, said switch having a member within saidhousing for moving the switch between said positions which member isoperable from outside said housing, a locking device interengaging saidcap of said housing and movable between a first position at which saidcap is locked at a desired location against rotation and a secondposition at which said cap is free to be rotated to unthread the cap forremoval to expose said opening, said locking device being operable fromoutside said housing, the improvement comprising: interlocking meansoperatively interconnecting the switch operating member and said caplocking device for retaining said locking device in said first positionso long as the member is in the switch-closed position while freeing thelocking device for movement to the second position so long as the memberis in the switch-open position, and for normally blocking the member formovement from switch-open to switch-closed position so long as the capis off the body, said interlocking means including a sensor positionedto be contacted by said cover and in a first position when said cover isin place and to be moved to a second position when said cover is off thebody; said locking device including a first pin in said body and movablein a direction generally parallel to the axis of the threads between ablocking position and an unblocking position, said cap having abutmentmeans positioned adjacent the pin when the cap is in place and said pinis in the blocking position to prevent rotation of the cap to unthreadthe cap from the body, resilient means bearing on the pin to urge thepin to said blocking position, said pin being movable against saidresilient means to said unblocking position at which said cap may berotated; said sensor including a second pin on said body, movable in adirection generally parallel to the axis of the threads and positionedso that one end of the second pin will contact said cap when said cap isin place, resilient means bearing against the second pin and urging itin the direction of said one end, whereby said second pin is held in afirst position by the pressure of said cap when the cap is in place andis moved to a second position by the last-mentioned resilient means whenthe cap is removed; and said interlocking means including a platemovable in said housing and having portions adjacent said pins, saidplate being connected to said member.
 2. In an apparatus as set forth inclaim 1, wherein said pins each have a longitudinal axis, said platebEing movable in a plane intersecting said axes between a first positionat which the member is in the switch-closed position and a secondposition at which the member is in the switch-open position, said platehaving a closed area aligned with the axis of the first pin when themember is in the switch-closed position with said closed area beingpositioned to block movement of the first pin from the blocking to theunblocking position, said plate having an open area aligned with theaxis of the first pin when the member is in the switch-open positionwith said open area unblocking said first pin so that it may be moved tothe unblocking position, said second pin having an abutment thereonwhich abutment is moved with the second pin, said abutment beingpositioned to block the movement of the plate from the switch-open tothe switch-closed position when the second pin is in its secondposition, said abutment being moved to an unblocking position when thesecond pin is moved to the first position.
 3. In an apparatus as setforth in claim 2, wherein said cap has a flange thereon, said abutmentmeans being in the side of said flange adjacent said body, said flangehaving a small opening extending from said abutment means to the otherside of the flange, whereby a small object may be inserted through saidsmall opening to move the first pin from the blocking to the unblockingposition.
 4. In an apparatus as set forth in claim 2, wherein as saidcap is moved toward said desired location by the rotation of said capand said second pin is being moved from said second position toward saidfirst position to release said plate, said first pin is simultaneouslybeing moved by the cap into a position at which it blocks the movementof the plate until the cap reaches said desired location and the firstpin engages said abutment means thereby moving the first pin out ofblocking position to free said plate.
 5. In an apparatus as set forth inclaim 1, wherein said cap has a flange thereon, said flange having arecess in the side of said flange adjacent said body and defining saidabutment means, said flange having a small opening extending from saidrecess to the other side of the flange, whereby a small object may beinserted through said small opening to move the first pin from theblocking to the unblocking position.